THE ROLE OF OXYGEN IN PHOTOSENSITIZATIONS WITH POLYACETYLENES AND THIOPHENE DERIVATIVES

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Abstract
Abstract— The mechanism of photosensitization by polyacetylenes and biosynthetically derived thiophenes from species of the plant family Asteraceae was examined. With thiophenes photosensitization of yeast and E. coli occurred under aerobic but not anaerobic conditions. For similar experiments with polyacetylenes, both photodynamic and non‐photodynamic mechanisms were observed. While the relative toxicities of thiophenes and polyacetylenes under near UV radiation was in general similar, the in vitro generation of singlet oxygen was considerably less for polyacetylenes than thiophenes, which is additional evidence for the existence of an alternate mechanism of action in polyacetylene photosensitization. Rates of photodegradation of polyacetylenes are higher than for thiophenes suggesting that bond breaking/formation processes are more favored relative to energy transfer to oxygen for polyacetylenes than thiophenes.